I like to send PDF as it guarantees formatting is retained, as you've stated. But if you're going through an agent, they'll most likely want to remove your personal details and add their letterhead so they won't accept PDF.

If sending to an agency, you can always send two versions - one for them with all your contact details on and one with all that removed (although worth finding out exactly what they would want retained)

The only time I've given up trying to read a CV is when it required signing up to be there friend on some document sharing website. I think they were trying to be clever. Our secretary wrote back and asked for a doc or pdf.

I only use openoffice at work but I send things as PDF to be sure of formatting.

Also, one of the job sites - can't remember which, is really crap for the auto cover letter it sends. I put an advert out and got about 200 applicants. Most had stored a profile and this produced a cover summary. If when they first registered they were looking for something specific like forklift driving, admin role, biochemical research but had now broadened their searching the cover letter still put "Looking for : xxx". Which left me with an easy way to cull the 200 - thrown out those who didn't update their profile. As it was, I skimmed all 200, but not everyone will.